Electrorheological suspensions

The objective of this article is to give a review of electrorheological (ER) suspensions whose rheological properties can abruptly change under an external electric field. Attention is given to the physical backgrounds behind ER phenomena reported recently. The criteria on how to design a high performance ER fluid and mechanisms explaining how an ER suspension displays the ER effect are focused upon. We begin with a brief historic introduction, ER materials, followed by positive ER effect, negative ER effect and photo-ER effect discussions. The physical parameters that can substantially affect the ER effect are discussed thereafter, and physical processes occurring in ER suspensions under an electric field are reviewed. The mechanisms of the ER effect proposed before are summarized. A future outlook on the ER material development and ER fluid applications is given.